/*
 * Copyright (c) 1988 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * High level routines dealing with getting lines of input 
 * from the file being viewed.
 *
 * When we speak of "lines" here, we mean PRINTABLE lines;
 * lines processed with respect to the screen width.
 * We use the term "raw line" to refer to lines simply
 * delimited by newlines; not processed with respect to screen width.
 */

#include <sys/types.h>
#include <less.h>

extern int squeeze;
extern int sigs;
extern char *line;

off_t ch_tell();

/*
 * Get the next line.
 * A "current" position is passed and a "new" position is returned.
 * The current position is the position of the first character of
 * a line.  The new position is the position of the first character
 * of the NEXT line.  The line obtained is the line starting at curr_pos.
 */
off_t
forw_line(curr_pos)
        off_t curr_pos;
{
        off_t new_pos;
        register int c;

        if (curr_pos == NULL_POSITION || ch_seek(curr_pos))
                return (NULL_POSITION);

        c = ch_forw_get();
        if (c == EOI)
                return (NULL_POSITION);

        prewind();
        for (;;)
        {
                if (sigs)
                        return (NULL_POSITION);
                if (c == '\n' || c == EOI)
                {
                        /*
                         * End of the line.
                         */
                        new_pos = ch_tell();
                        break;
                }

                /*
                 * Append the char to the line and get the next char.
                 */
                if (pappend(c))
                {
                        /*
                         * The char won't fit in the line; the line
                         * is too long to print in the screen width.
                         * End the line here.
                         */
                        new_pos = ch_tell() - 1;
                        break;
                }
                c = ch_forw_get();
        }
        (void) pappend('\0');

        if (squeeze && *line == '\0')
        {
                /*
                 * This line is blank.
                 * Skip down to the last contiguous blank line
                 * and pretend it is the one which we are returning.
                 */
                while ((c = ch_forw_get()) == '\n')
                        if (sigs)
                                return (NULL_POSITION);
                if (c != EOI)
                        (void) ch_back_get();
                new_pos = ch_tell();
        }

        return (new_pos);
}

/*
 * Get the previous line.
 * A "current" position is passed and a "new" position is returned.
 * The current position is the position of the first character of
 * a line.  The new position is the position of the first character
 * of the PREVIOUS line.  The line obtained is the one starting at new_pos.
 */
off_t
back_line(curr_pos)
        off_t curr_pos;
{
        off_t new_pos, begin_new_pos;
        int c;

        if (curr_pos == NULL_POSITION || curr_pos <= (off_t)0 ||
                ch_seek(curr_pos-1))
                return (NULL_POSITION);

        if (squeeze)
        {
                /*
                 * Find out if the "current" line was blank.
                 */
                (void) ch_forw_get();   /* Skip the newline */
                c = ch_forw_get();      /* First char of "current" line */
                (void) ch_back_get();   /* Restore our position */
                (void) ch_back_get();

                if (c == '\n')
                {
                        /*
                         * The "current" line was blank.
                         * Skip over any preceeding blank lines,
                         * since we skipped them in forw_line().
                         */
                        while ((c = ch_back_get()) == '\n')
                                if (sigs)
                                        return (NULL_POSITION);
                        if (c == EOI)
                                return (NULL_POSITION);
                        (void) ch_forw_get();
                }
        }

        /*
         * Scan backwards until we hit the beginning of the line.
         */
        for (;;)
        {
                if (sigs)
                        return (NULL_POSITION);
                c = ch_back_get();
                if (c == '\n')
                {
                        /*
                         * This is the newline ending the previous line.
                         * We have hit the beginning of the line.
                         */
                        new_pos = ch_tell() + 1;
                        break;
                }
                if (c == EOI)
                {
                        /*
                         * We have hit the beginning of the file.
                         * This must be the first line in the file.
                         * This must, of course, be the beginning of the line.
                         */
                        new_pos = ch_tell();
                        break;
                }
        }

        /*
         * Now scan forwards from the beginning of this line.
         * We keep discarding "printable lines" (based on screen width)
         * until we reach the curr_pos.
         *
         * {{ This algorithm is pretty inefficient if the lines
         *    are much longer than the screen width, 
         *    but I don't know of any better way. }}
         */
        if (ch_seek(new_pos))
                return (NULL_POSITION);
    loop:
        begin_new_pos = new_pos;
        prewind();

        do
        {
                c = ch_forw_get();
                if (c == EOI || sigs)
                        return (NULL_POSITION);
                new_pos++;
                if (c == '\n')
                        break;
                if (pappend(c))
                {
                        /*
                         * Got a full printable line, but we haven't
                         * reached our curr_pos yet.  Discard the line
                         * and start a new one.
                         */
                        (void) pappend('\0');
                        (void) ch_back_get();
                        new_pos--;
                        goto loop;
                }
        } while (new_pos < curr_pos);

        (void) pappend('\0');

        return (begin_new_pos);
}
